The present invention relates to a new and improved method for the preservation of activated sludge for the reuse in waste water purification stages working according to the activated sludge process, wherein the activated sludge, which is to be preserved, is flushed with gas.
In the event that waste water purification stages must operate, in accordance with the activated sludge process, with pronounced fluctuating loads, with the band width of such fluctuations being relatively long, for instance amounting to a number of days, or if such waste water purification stages experience an interruption in the infeed of the raw waste water or sewage, in the order of equally a number of days, then upon sudden loading of the system or restarting thereof difficulties arise, because the aerobic microorganisms required for realizing the requisite degree of purification, are not available in the required amounts or with the necessary activity. During a relatively long start-up time such type stages therefore operate at reduced efficiency. In order to overcome this limitation it is known from German patent No. 2,446,289 and the article of J. Gnieser, entitled "Der spezifische Sauerstoffbedarf als Regelgrosse fur aerobe biologische Systeme" (roughly translated as: "The Specific Oxygen Requirement as a Regulating Magnitude for Aerobic Biological Systems"), appearing in the publication "Chemische Rundschau", No. 6/1978, to store the excess active sludge which is always formed during the normal operation in a container and by aeration as well as, if needed, by the addition of nutrients to retain such active. When necessary, this sludge then can be again infed into the purification stage as additional activated sludge. If this reserve quantity of activated sludge is not continuously exchanged, because for instance there has arisen an interruption in the waste water or sewage, then there is required the addition of nutrients in conjunction with aeration, since otherwise the active retained biological mass would become continuously smaller due to self-respiration.
Preparation of the system components needed for the infeed of nutrients and the method operations during the nutrient infeed itself, require an additional expenditure for such type installations and processes.